From 1d3908410bdf8f87cba7501c4b022bc901ebd535 Mon Sep 17 00:00:00 2001
From: Brion Vibber <brion@pobox.com>
Date: Fri, 24 Mar 2023 01:18:49 -0700
Subject: [PATCH] using the 'pal' colors is closer? why????

---
 dither-image.js | 42 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/dither-image.js b/dither-image.js
index ebe7faf..1bf07af 100644
--- a/dither-image.js
+++ b/dither-image.js
@@ -68,6 +68,39 @@ class RGB {
         return new RGB(r,g,b);
     }
 
+    static fromGTIA(val) {
+        // This seems off from what Atari800 does
+        // https://forums.atariage.com/topic/107853-need-the-256-colors/page/2/#comment-1312467
+        let cr = (val >> 4) & 15;
+        let lm = val & 15;
+        let crlv = cr ? 50 : 0;
+
+        /*
+        let phase = ((cr - 1) * 25 - 58) * (2 * Math.PI / 360);
+
+        let y = 255 * (lm + 1) / 16;
+        let i = crlv * Math.cos(phase);
+        let q = crlv * Math.sin(phase);
+
+        let r = y + 0.956 * i + 0.621 * q;
+        let g = y - 0.272 * i - 0.647 * q;
+        let b = y - 1.107 * i + 1.704 * q;
+        */
+
+        // PAL
+        let phase = ((cr - 1) * 25.7 - 15) * (2 * Math.PI / 360);
+
+        let y = 255 * (lm + 1) / 16;
+        let i = crlv * Math.cos(phase);
+        let q = crlv * Math.sin(phase);
+
+        let r = y + 0.956 * i + 0.621 * q;
+        let g = y - 0.272 * i - 0.647 * q;
+        let b = y - 1.107 * i + 1.704 * q;
+
+        return new RGB(r, g, b).clamp().fromSRGB();
+    }
+
     map(callback) {
         return new RGB(
             callback(this.r),
@@ -166,6 +199,7 @@ class RGB {
     }
 }
 
+/*
 // snarfed from https://lospec.com/palette-list/atari-8-bit-family-gtia
 // which was calculated with Retrospecs App's Atari 800 emulator
 let atariRGB = [
@@ -427,6 +461,14 @@ let atariRGB = [
     0xffff99,
 ].map((hex) => RGB.fromHex(hex).fromNTSC());
 //].map((hex) => RGB.fromHex(hex));
+*/
+
+let atariRGB = [];
+for (let i = 0; i < 256; i++) {
+    atariRGB[i] = RGB.fromGTIA(i);
+}
+
+
 
 /**
  * Dither RGB input data with a target palette size.